Traveling wave tubes



y 1960' w. s. GEISLER, JR 2,939,045

TRAVELING WAVE TUBES 2 Sheets-Sheet 1 Filed May 12, 1954 &, INVENTQR.

Wilson 5: Gels/95.11.

pm 5 5 am Palnnf Agent y 1960 w. s. GEISLER, JR 2,939,045

TRAVELING WAVE TUBES Filed May 12, 1954 2 Sheets-Sheet 2 Fig.3 T 34INVENTQR. Wilson 53 GG'ISIELJI.

Patent Agent United States Patent Q TRAVELING WAVE TUBES Wilson S.Geisler, Jr., Atherton, Calif, assignor, by mesne assignments, toApplied Radiation Corporation, Walnut Creek, Califi, a corporation ofCalifornia Filed May 12, 1954, Ser. No. 429,265

Claims. (Cl. SIS-39.3)

This invention relates to electron discharge devices and moreparticularly, to traveling wave tubes operable at microwave frequenciesas broad band amplifiers.

Since traveling wave tubes are of comparatively recent vintage, littlework has been done except on theoretical and experimental investigation.As a consequence, the traveling wave tubes themselves, the arrangementfor coupling the microwave frequency energy into and out of the tubes,and the arrangement for focusing the electron beam, have been somewhatinefiicient and in most cases, excessively cumbersome.

Accordingly, it is an object of the present invention to provide atraveling wave tube arranged in combination with radio frequencycouplers and focusing means as a compact and efiicient unit or package.

A feature of the invention involves the provision of a traveling wavetube unit having integrated means for establishing the required externalelectrical connections with utmost facility.

Another feature involves the provision of an improved arrangement forphysically mounting a traveling wave tube or similar electron dischargedevice.

A further feature is the provision of a novel and particularly effectivearrangement for coupling radio frequency energy into and out of atraveling wave tube.

A further feature involves the provision of an eifective yet simpleattenuator for utilization with such a tube.

Additionally, a feature of the invention is directed to the actualstructural features of the tube which facilitate both the assembly andoperation.

Other features of the invention, as well as the advantages obtainedtherefrom will become readily apparent from the following descriptiontaken in conjunction with the accompanying drawings, wherein:

Figure 1 is a side view in elevation of a traveling wave tube unit orpackage embodying the present invention, with a portion of the outerhousing broken away to illustrate interior details of the construction,

Figure 2 is a longitudinal sectional view of the traveling wave tubebefore its incorporation in the package,

Figure 3 is a transverse section of the traveling wave tube unit takenalong line 3--3 of Figure 1 and illustrating the manner in which thecoupling and focusing means are joined physically to the tube, i

Figure 4 is a fragmentary section taken along line 4 -4 of Figure 3, and

Figure 5 is a longitudinal section of a central portion of the unitshowing details of an attenuator structure.

As most clearly illustrated in Figure 2, the traveling wave tubeconstructed in accordance with the present invention includes anelongated glass body 1d of small tubular cross section throughout mostof its length but enlarged at one end as indicated at 11 to enablemounting of an electron gun 12. Within the glass tube It} a slowwavestructure in the form of a metal helix 13 is disposed to provide thedesired interaction between the electrons which emerge as a beam fromthe electron gun 12 and f. ICE

the radio frequency wave applied to the helix 13 in a manner to bedescribed hereinafter.

structurally, the helix 13 is provided at one end with a small hook 14and at the other is spotwelded to a metal base 15 which preferably takesthe form of a short cylindrical stub 16 substantially equal in diameterto the helix and having an annular ring 17 brazed to its exterior. Thedescribed tubular glass body 10 is formed upon an accurately machinedmandrel so that its inner diameter closely corresponds to the outerdiameter of the helix 13 and thus enables slidable insertion, yetsubsequent support of the latter. The hooked end 14 of the helix 13 isinserted into the body 10 at its enlarged end 11 and is pushedtherethrough until the annular ring portion 17 of the described helixbase 15 comes into engagement with the shoulder formed at the enlargedend 11 of the glass body. The hooked end 14 of the helix is then pulledand brought into hooked engagement over the other end of the glass body10 and is subsequently engaged by a small metal tubulation 18 sealed tothe end of the body. Such engagement maintains the helix 13 permanentlyin its slightly stretched position and establishes electrical connectionbetween the helix and the tubulation. The geometry of the helix 13 issuch that when secured in the manner described, the phase velocity ofthe applied radio frequency wave along the axis corresponds very closelyto the velocity of the electrons injected from the electron gun 12.

The electron gun 12 is generally of conventional construction includinga cathode 20 supported by means of an annular ceramic spacer 21 on theinterior of a cupshaped body 22. The side wall of the gun body 22 isformed of a pair of copper cylinders 23, 23" having lateral flangesbrazed together and to the end of one cylinder 23 a first anode 24in theform of a copper cup is brazed so that a central opening therein liesadjacent and axially aligned with the cathode 20. The electron gun 12 ismounted so that the cathode 20 and first anode 24 are aligned with theaxis of the helix 13, such mounting being accomplished by means of acopper cylinder 25 secured at one end to the exterior of the gun body22, as by brazing, and being supported at its other end in vacuum-tightrelation on the end of the enlarged portion 11 of the glass body 10. Thebase of the cup-shaped gun body 22 is formed by aceramic disc 26 whichis sealed to the end of the cylinder 23' of the gun body 22 and supportsin vacuum-sealing relation wires 27, 28, 29 which extend therethrough toenable application of voltage to the oathode 20, to a filament 30 forheating the cathode, and additionally, to a conventional getter 31,which can be fired subsequent to evacuation of the traveling wave tubeto purge all remaining impurities.

Evacuation of the tube is accomplished, in accordance with the presentinvention, through the previously described tubulation 18 at its distalend. After the tube has been pumped through this tubulation, it iscarefully pinched off, as shown in the drawing, to subsequently serve asa collector for the spent electrons which have traversed the full lengthof the tube.

Brazed to the exterior of the gun body 22 is an annular disc 32 whichcontrols the longitudinal disposition of the traveling wave tube withina cylindrical housing 33 that is adapted to receive the tube. Inaccordance with the present invention, this housing 33 not only servesas a protective cover for the traveling wave tube but also mounts withinits interior the meansfor focusing the electron beam within thetraveling wave tube and the means for coupling radio frequency energyinto and out of the tube. The arrangement is such that the tube wheninserted, is held in proper spaced relation to the focusing means. i

As best shown in Figure 1, this housing 33 constitutes an elongatedmetal tube as of steel, such metal tube being provided with a number ofopenings enabling radio frequency input and output connections to bemade therethrough and additionally, enabling the insertion of cap screws34. At each of three points'longitudinally of the tubular housing 33,three of the cap screws 34 are inserted in the openings which arepreferably disposed at circumferential intervals of approximately 120degrees. Each screw 34 is adapted to enter a registering threaded boreextending radially through the dividing portions 35 on a partitionedbrass spool 36 upon which are wrapped wires to form coils 37 thatconstitute the aforementioned focusing means (for the traveling wavetube. This spool 36, after slidable insertion into the tubular housing33 so that the threaded bores thereof register with the describedopenings in the housing, is then clamped securely within the housing bythe cap screws 34.

As best shown in Figures 3 and 4, the cap screws 34 project only a shortdistance into the threaded bores of the brass spool, and set screws 38projecting inwardly from the bores are adapted to engage and supportthrough such engagement, small tubular non-magnetic metal housings 39for axially spaced input and output couplers and a generally similarhousing 39 for an attenuator' disposed intermediately thereof. These setscrews 38 are held in position by lock screws 40 dis- .posed at anintermediate position in the threaded bores in the spool 36.

Within each coupler housing 39, a tubular electrostatic shield 41 issupported and itself encompasses a coupling helix 42 of a diameter suchthat a traveling wave tube can be inserted thereinto. The pitch of thecoupling helix 42 is arranged so that the phase velocity of radiofrequency energy applied thereto is substantially equivalent to thephase velocity of the helix 13 within the inserted traveling wave tube.The electrostatic shield 41 is maintained in spaced relation to thecoupling helix 42 by insulation 43 such as Teflon, so as to constitute,in efli'ect, a section of coaxial transmission line having an impedancedetermined by the length of the section. The length is chosen, inaccordance With the present invention, to produce an impedance valueequivalent to that of the feed line for the input or output couplers.This feed line, as shown in Figure 3, constitutes a coaxial cable 44,the inner conductor 45 of which is soldered to one end of the couplinghelix 42 and passes outwardly through a radial opening in the couplerhousing 39 and the outer conductor 46 of which is soldered to thecoupler housing 39. The shield 41, the insulation 43, and the couplinghelix 42 are maintained within the coupler housing 39 by means ofpacking glands at the ends thereof. Each gland constitutes a rubberwasher 47 which is pressed against the end of the coupling helix 42 andthe surrounding insulation 43 and shield 41 by an annular nut 48, whichmay be screwed into the threaded interior ends of the coupler housing39.

The two couplers and the attenuator are adapted to closely encompass aninserted traveling wave tube and upon tightening of the packing nuts 48,the washers 47 are squeezed so that they resiliently engage the glassbody 10. Since the couplers and the attenuator are supported by thedescribed set screws 38 held by the lock screws 40, the disposition ofthe traveling wave tube within the outer cylindrical housing 33 and moreparticularly, within the focusing coils 37 may be securely maintained.To adjust the axial disposition of the traveling wave tube, one or moreof the cap screws 34 and the lock screws 40 are removed and therespective set screws 38 areturned to effect displacement of all ormerely one portion of the traveling wave tube, as desired, to place thetube in properly spaced relation to the focusing coils 37. Thereafter,the lock screws 40 and capscrews 34 are reinserted to hold the unitsecurely in its adjusted position.

The intermediately mounted attenuator is similar in construction to theinput and output couplers, like parts being indicated by like numeralswith an added prime notation. They ditfer only in the facts that a layer49 of aquadag or other lossy material is applied to the exterior surfaceof the insulation 43' and of course, that any exterior radio frequencyconnection is omitted. This type of attenuator is to be preferred overthe normal or conventional type, which merely constitutes a coating ofaquadag applied to the exterior of the glass tube, in that it provideseffectively a more concentrated attenuation and eliminates the so-calledtube effect which deleteriously affects the phase velocity of the radiofrequency wave within the traveling wave tube.

The coaxial cables 44 connected to the input and output couplers passradially outward from the coupler housings 39 through radial bores inthe brass spool 36 and terminate in conventional coaxial connectors 50.A suitable packing gland 51 is applied to each coaxial cable 44exteriorly of the outer housing 33 both to provide support for the cable44 and to establish electrical ground connection between the outerconductor of the cable 44 and the housing 33-.

After the traveling wave tube has been inserted into the housing 33 soas to be encompassed by each of the input and output couplers, as wellas by the intermediate attenuator, and the packing nuts 48 are tightenedto provide the described resilient support, the previously describedannular disc 32 on the gun body 22 is then secured by screws 52 to theends of the spool 36, supporting the focusing coils 37, thus to maintainas previously mentioned, the longitudinal disposition of the travelingwave tube within the housing 33. Thereafter,

one end of the outer housing 33 is closed by a metal cap 53 and theother end is provided with an insulated socket 54 to which leads fromthe various electrical elements of the traveling wave tube may beconnected to thereby facilitate connection of exterior electrical powerto energize the tube.

The described first anode 24 is tied through the copper side wall of theelectron gun body 22 and the mounting disc 32 to the outer housing 33which is, as previously mentioned, maintained at ground potential. Thecathode and heater wires 28, 29 which emerge from the ceramic base 26 ofthe electron gun 12 are secured to suitable leads which pass between thefocusing coils 37 and the outer housing 33 for connection individuallyto prongs (not shown) in the insulated socket 54 at the other end of thehousing, the cathode wire 27 being adapted for connection to a DC.supply which maintains it at 300 volts negative relative to thedescribed first anode 24. Another wire 55 connected between the socket54 and the collector 18 at the end of the traveling wave tube is adaptedto supply a positive potential of approximately 2500 volts to thecollector 18 and to the helix 1'3 and its base 15 which, in effect,provides the second anode for the traveling wave tube. When the power issupplied to these connections by a suitable plug (not shown) and theradio frequency energy is supplied to the input coaxial connector 50,the beam in its traverse of the traveling wave tube interacts with theradio frequency wave so applied to amplify the same in the well-knownmanner and the amplified output is extracted through the output coaxialcable 44 and its connector 50. The intermediately positioned attenuatoracts effectively to preclude oscillation within the tube in a well-knownmanner, the incorporated shield 41' serving to enhance the effect of theaquadag layer 49.

It is apparent that the traveling wave tube unit, as described, requiresonly simple radio frequency input and output connections to the coaxialconnectors 50 and direct current voltage connections to the insulatedsocket 54 on the housing 33 to enable operation. Consequently, the useof this traveling wave device is facilitated and because of theprotected resilient mounting of the fragile glass body 10 of the tube,installation is enabled at points where vibration or other factors wouldnormally prohibit such use. Additionally, because of the steelconstruction of the housing 33, stray magnetic fields cannot enter todefocus the beam in the traveling wave tube.

Various modifications and alterations may obviously be made in eitherthe construction of the unit or the traveling wave tube itself withoutdeparting from the spirit of the presentinvention. For example, themounting arrangement embodied in the described unit might well beutilized for supporting a backward wave oscillator of generally similarconstruction. Consequently, the foregoing description and theaccompanying drawings are to be considered as purely exemplary and notin a limiting sense, the scope of the invention being indicated by theappended claims.

What is claimed is:

1. Mounting arrangement for a traveling wave tube comprising a housing,magnetic focusing means fixedly mounted within said housing, radiofrequency couplers within said focusing means and adapted to encompassand resiliently engage the tube adjacent the input and output endsthereof, and means for adjustably supporting said couplers from saidhousing in spaced relation to said focusing means.

2. Mounting arrangement for a traveling wave tube according to claim 1wherein said couplers include a resilient washer, and means for urgingsaid washer into supporting engagement with an encompassed travelingwave tube.

3. Mounting arrangement for a traveling wave tube comprising radiofrequency couplers adapted to encompass and resiliently engage atraveling wave tube adjacent the input and output ends thereof, magneticfocusing means encompassing said couplers, and means on said focusingmeans for individually adjusting the disposition of said couplerswhereby the encompassed tube can be shifted relative to said focusingmeans.

4. Mounting arrangement for a traveling wave tube according to claim 3comprising coaxial cables connected to said couplers and extendingtransversely through said focusing beams.

5. Mounting arrangement for a traveling wave tube having an elongatedbody with a slow wave structure therein, which arrangement comprises atubular housing adapted to encompass a traveling wave tube and havingapertures therein adjacent the ends of the slow wave structure therein,radio frequency couplers surrounding the tube adjacent the ends of theslow wave structure, coaxial cables for each coupler extendingtransversely therefrom through the openings in said housing, focusingmeans in the housing encompassing said tube and said couplers, and asocket at one end of said tubular housing and adapted to provideelectrical connection with the encompassed traveling wave tube and withsaid focusing means.

References Cited in the file of this patent UNITED STATES PATENTS2,541,843 Tiley Feb. 13, 1951 2,580,007 Dohler et al Dec. 25, 19512,584,802 Hansell Feb. 5, 1952 2,610,308 Touraton et al Sept. 9, 19522,636,948 Pierce Apr. 28, 1953 2,645,737 Field July 14, 1953 2,653,301Moore et al Sept. 22, 1953 2,701,321 Rich Feb. 1, 1955 2,774,006 Fieldet al. Dec. 11, 1956 2,782,339 Nergaard Feb. 19, 1957 2,797,353 Molnaret al June 25, 1957 2,828,434 Klein et al. Mar. 25, 1958 2,849,651Robertson Aug. 26, 1958

